v0.1.16

Release 0.1.16

Namespace every error code as E__

The convention was announced and not kept: 115 framework codes across ten
packages carried no E_ prefix, so an application filtering on the documented
rule handled some failures and missed others.

Blanket-prefixing them was the wrong fix, and trying it proved why — it made
E_FORBIDDEN mean three different things across ream, relay and warden, which
is worse than the inconsistency it replaced. The namespace after E_ is what
tells them apart.

Where a package already prefixed inside its error constructor — atlas, rune,
warden, and ream's module classes — the constructor now emits E__ and the
call sites stay bare, so the rule lives in one place per package instead of at
every throw. Each of those constructors passes through a code that already
starts with E_, which is how the upstream identifiers keep their exact
spelling: E_UNAUTHORIZED_ACCESS, E_INVALID_CREDENTIALS and E_VALIDATION_ERROR
are the ones a consumer branches on, and two packages naming the same upstream
failure legitimately share one.

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Changes since v0.1.15.